Built-Up Roofing (BUR) Systems for BC Commercial Buildings: Are They Still Relevant?

Built-up roofing, often shortened to BUR, is one of the oldest commercial flat-roof systems still found across British Columbia. Many older warehouses, schools, strata buildings, and institutional properties in Metro Vancouver and the Fraser Valley still have some form of asphalt-and-gravel roof assembly in place.

That leaves many building owners and property managers with a practical question: is BUR still a smart choice today, or is it mostly a legacy system that should be replaced with something newer?

The short answer is that BUR can still be a viable option in the right application, but it is no longer the default answer for most BC commercial reroofing projects. In many cases, modern SBS modified bitumen roofing systems offer similar multi-layer protection with easier detailing, lighter assemblies, and more adaptable installation options.

For decision-makers planning capital work, the better question is not whether BUR is outdated. It is whether BUR is an appropriate fit for the building, the budget, the access constraints, and BC's wet climate.

What is a built-up roofing system?

A built-up roof is a multi-ply asphalt roofing system made from alternating layers of bitumen and reinforcing felts or ply sheets, finished with a protective surfacing layer. Industry groups such as ARMA and the Canadian Roofing Contractors Association describe BUR as a layered membrane assembly rather than a single sheet product.

A typical BUR assembly may include:

• roof deck
• vapor retarder where required
• insulation and cover board
• multiple plies of reinforcing felts
• hot-applied asphalt or approved adhesive between plies
• surfacing, often gravel, mineral cap sheet, or coating

Traditional BUR is often called a three-ply or four-ply roof, depending on how many reinforcing layers are used in the membrane.

That layered construction is the reason BUR developed such a strong reputation. If the top surface is damaged, the assembly still has backup layers below it. For large commercial roofs, that redundancy has real value.

Why BUR earned such a strong reputation

BUR became popular because it solved a basic commercial roofing problem well: keeping water out over large, low-slope roof areas.

Its long-standing advantages include:

Redundancy

Unlike single-ply systems, BUR is not relying on one membrane thickness alone. Multiple plies create multiple lines of defense.

Durability under traffic

Older commercial buildings often have frequent rooftop traffic from HVAC technicians, electricians, and other trades. A well-built BUR assembly can tolerate incidental traffic better than some thinner membranes, especially when properly surfaced and protected.

Proven track record

BUR has decades of field history across North America. In BC, many older asphalt-and-gravel roofs remained in service for years because the system was familiar, repairable, and forgiving when maintained.

Good fit for certain heavy-duty applications

Where the roof needs to accommodate equipment zones, service walk paths, or other hard-use conditions, a multi-ply bituminous assembly can still make sense.

Why BUR is less common on many modern BC projects

Even though BUR still has strengths, many commercial owners in the Lower Mainland, Fraser Valley, and Sea-to-Sky now choose SBS modified bitumen or other modern systems instead.

That shift is not because BUR suddenly stopped working. It is because newer systems often solve the same problems with fewer installation constraints.

Key reasons BUR is less common today include:

More labour-intensive installation

BUR is built in the field one layer at a time. That typically means more labour, more coordination, and tighter quality-control demands than some newer assemblies.

Heavier roof assemblies

Traditional asphalt-and-gravel BUR systems can add significant dead load. That matters on older buildings, especially during reroofing when structural capacity should be reviewed carefully before adding or changing assemblies.

More challenging detailing on complex roofs

Modern commercial roofs often have dense penetrations, curbs, drains, equipment rails, and phased work conditions. BUR can be detailed successfully, but modified bitumen systems often make those transitions simpler and more consistent.

Safety and site logistics

Hot-applied asphalt work requires additional safety controls, access planning, odour management, and staging. On occupied buildings in Metro Vancouver, those constraints can materially affect project planning.

Better alternatives for many use cases

For many BC reroofing scopes, SBS delivers the bituminous, multi-layer benefits owners want while offering better flexibility and often more practical installation methods.

How BUR compares to SBS modified bitumen

For most BC property managers comparing older built-up roofs with current options, this is the real decision point.

BUR and SBS both belong to the bituminous roofing family, but they are not the same system.

BUR

• field-built, ply-by-ply membrane
• typically uses hot asphalt and reinforcing felts
• often finished with gravel or other surfacing
• heavier and more traditional in assembly

SBS modified bitumen

• factory-manufactured sheets with polymer-modified asphalt
• often installed in two-ply assemblies
• generally offers better flexibility than traditional BUR
• commonly used on BC commercial reroofing projects

In practical terms

SBS is often seen as the evolution of traditional bituminous roofing. It keeps the redundancy and repairability many owners like, but it generally adapts better to modern detailing and BC weather conditions.

On a straightforward box warehouse with a large open roof area, BUR may still be defensible. On a complex occupied commercial building with multiple penetrations and access constraints, SBS is often the more practical recommendation.

For a broader membrane comparison, see Commercial Roofing Membrane Types: Complete Comparison Guide for BC Buildings.

Is BUR a good fit for BC's climate?

BC climate does not treat all roof systems equally. The province's commercial roofs deal with long wet seasons, repeated drainage stress, rooftop moss and organic growth, coastal humidity, and in some areas snow loading and freeze-thaw cycling.

BUR can perform well in this environment, but only when the full assembly is designed, installed, and maintained properly.

Where BUR can perform well in BC

BUR can still be a solid option when:

• the building has a large, relatively simple low-slope roof
• the structure can handle the assembly weight
• the detailing is straightforward
• there is a qualified crew with strong bituminous-system experience
• the owner values redundancy and ruggedness over a lighter assembly

Where BUR can struggle in BC

BUR becomes less attractive when:

• drainage is poor or ponding is already a recurring issue
• the building has many penetrations or frequent future alterations
• access is tight and kettle operations are difficult
• the property remains fully occupied during sensitive work
• the owner wants a lighter or easier-to-phase reroofing assembly

BC's wet climate makes drainage and detailing critical. If water sits on the roof, even a durable membrane can age faster. If the surfacing is compromised, UV and weather exposure can accelerate deterioration.

The province has also noted that climate change is contributing to more intense fall and winter storm patterns. That makes drainage design, maintenance access, and seasonal inspection discipline even more important for any low-slope roof system.

Related reading: Ponding Water on Commercial Roofs: Causes, Risks, and Solutions.

Where BUR still makes sense today

BUR is no longer the automatic answer, but it is not obsolete either. There are still cases where it can be the right fit.

1. Large simple roof areas

Big open roof plates with limited penetrations are often where BUR makes the most sense. The assembly benefits from repetition and fewer complicated details.

2. Buildings that value multi-layer toughness

Some institutional and industrial owners prefer the feel of a heavier, redundant assembly, especially where service traffic is common and rooftop equipment is substantial.

3. Projects with owners who understand bituminous maintenance

If the ownership group already manages bituminous roofs across a portfolio, BUR may fit existing maintenance practices and internal expectations.

4. Specific replacement-in-kind situations

On some older buildings, especially where the existing roof is BUR and the geometry is simple, a bituminous reroofing strategy may remain logical after structural review and condition assessment.

When BUR is usually not the best recommendation

In many modern reroofing projects, BUR is not the most efficient or flexible choice.

Complex roof layouts

The more penetrations, curbs, drains, changes in elevation, and future tenant-improvement work a roof has, the more likely a modern SBS system will be easier to execute and maintain.

Occupied buildings with disruption sensitivity

Retail, office, strata, institutional, and healthcare buildings often need careful phasing, odour control, and predictable site logistics. Traditional hot-applied BUR work can create more coordination demands.

Buildings with structural load concerns

Not every older deck can comfortably accept a heavier assembly. Before considering any new roof, especially a traditional asphalt-and-gravel system, the existing structure and dead-load implications should be reviewed.

Owners seeking easier future modifications

If new HVAC units, vents, solar supports, or other penetrations are likely in coming years, a more modern system may offer cleaner future integration.

What BC building owners should evaluate before choosing BUR

A roof-system decision should be based on the building, not habit alone.

Before selecting BUR for a BC commercial project, it helps to evaluate the following.

Building use and occupancy

• Is the building fully occupied during construction?
• Are there odour-sensitive uses inside?
• Will operations continue normally during the work?

Roof complexity

• How many penetrations, drains, and edge conditions exist?
• Are there a lot of curbs, sleepers, and service corridors?
• Is future rooftop equipment likely?

Structural capacity

• What is on the roof now?
• Can the deck and structure support the proposed replacement assembly?
• Is a recover being considered, or is full tear-off more appropriate?

Drainage performance

• Does the roof already pond water?
• Are drains, scuppers, and slopes working properly?
• Would tapered insulation or drainage redesign provide better value than simply replacing membrane?

Contractor and specification quality

BUR is not just a material choice. It is a workmanship-intensive system. The quality of specification, substrate preparation, bitumen application, flashing execution, and surfacing all matter.

Cost and lifecycle considerations

BUR is sometimes assumed to be the low-cost option because it is traditional. That is not always true.

In current-market reroofing, BUR may be competitive in some straightforward applications, but labour intensity, access constraints, and building complexity can quickly change the economics.

General considerations include:

• initial costs vary based on tear-off scope, insulation changes, deck repairs, access, and surfacing type
• heavier assemblies may have structural implications that affect total project cost
• long-term value depends heavily on drainage, detailing, and maintenance discipline
• on some projects, SBS provides similar long-term performance with a more practical installation path

Any budget numbers should be treated as project-specific, not universal. Actual pricing varies significantly by building size, specification, access, occupancy constraints, and market conditions.

Maintenance realities for existing BUR roofs in BC

A large number of BC buildings still have aging BUR systems in service. Even if replacement is not immediate, these roofs need disciplined maintenance.

Priority maintenance items include:

• clearing drains and scuppers before and during storm season
• checking gravel loss or surfacing wear in exposed areas
• monitoring flashings, edge details, and penetrations
• watching for blisters, splits, ridging, and exposed asphalt
• documenting wet areas and leak patterns before they spread

On older roofs in Metro Vancouver and the Fraser Valley, moss, debris accumulation, and blocked drainage often create as many problems as the membrane itself.

A condition assessment should answer three key questions:

1. Is the existing BUR still serviceable?
2. Are targeted repairs realistic, or is deterioration too widespread?
3. If replacement is required, should the next system still be BUR, or is SBS or another assembly a better fit?

If replacement is being considered, a professional commercial reroofing review should look beyond just the membrane surface. Drainage design, insulation strategy, edge details, and rooftop traffic patterns all affect long-term performance.

So, are BUR systems still relevant for BC commercial buildings?

Yes, but selectively.

BUR still has a place in commercial roofing because multi-ply redundancy, durability, and proven service history still matter. But on many present-day BC projects, it is no longer the most practical or versatile choice.

For many owners, the more useful question is not traditional BUR versus no BUR. It is whether a modern bituminous system, especially SBS modified bitumen, can deliver the protection they want with fewer project constraints.

That decision should be based on:

• building complexity
• occupancy sensitivity
• structural capacity
• drainage conditions
• long-term maintenance goals
• installer experience with the specified assembly

In short, BUR is still relevant, but it should be chosen deliberately, not by default.

CTA: Get the right bituminous roofing recommendation for your building

If your building has an aging asphalt-and-gravel roof, or if you are weighing BUR against newer systems, Raven Roofing can help assess the building, the existing assembly, and the most practical path forward.

Our team works with commercial and strata properties across the Metro Vancouver service area, the Fraser Valley, and the Sea-to-Sky corridor to evaluate reroofing options based on real site conditions, not generic product claims.

To discuss a replacement strategy, inspection, or bituminous system recommendation, contact Raven Roofing to review your roof and project goals.

Frequently asked questions about BUR roofing in BC

Is built-up roofing the same as modified bitumen?

No. Both are bituminous roof systems, but BUR is a traditional field-built multi-ply assembly, while modified bitumen uses factory-manufactured sheets, often in two-ply systems such as SBS. Modified bitumen is often more flexible and easier to detail on complex roofs.

How long can a BUR roof last in BC?

Service life depends on design, drainage, workmanship, rooftop traffic, maintenance, and exposure. Well-built BUR systems can last for many years, but aging BC roofs should be evaluated based on current condition rather than assumed lifespan.

Is BUR still used on new commercial roofs?

It is still used in some applications, but it is less common than it once was. Many new or replacement low-slope projects now favour SBS modified bitumen or other membrane systems because they can be easier to detail and install.

Should an old BUR roof be repaired or replaced?

That depends on moisture intrusion, surfacing loss, flashing condition, drainage performance, and how widespread the deterioration is. A roof inspection can determine whether targeted repairs are still sensible or whether replacement planning is the better move.